Based on the theory of Jones matrix, a model for the analysis of non-PM fiber ring lasers polarization characteristics was developed. The model was further tested by experiments. From the numerically and experimentally analysis results, it was found that lasers composed of non-PM fiber can achieve stable output but its polarization varied with external perturbation. If polarizer was inserted into the laser cavity, the instability of output and polarization was even more serious. So special polarization control must be performed to obtain single polarization laser output using non-PM fiber.